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FOUS11 KWBC 180952
QPFHSD
 
PROBABILISTIC HEAVY SNOW AND ICING DISCUSSION
NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD
451 AM EST FRI JAN 18 2008
 
VALID 12Z FRI JAN 18 2008 - 12Z MON JAN 21 2008
 
DAY 1...

UPPER GREAT LAKES...

STRONG COLD ADVECTION OVER THE RELATIVELY WARM OPEN WATERS OF
LAKES SUPERIOR AND MICHIGAN WILL SET UP LAKE ENHANCED SNOWS OVER
THE UPPER PENINSULA OF MI AND WESTERN/NORTHERN LOWER MICH LATER
TODAY AND TONIGHT DUE TO STEEP LOW LEVEL LAPSE RATES AND NEARLY
UNIDIRECTIONAL WIND PROFILE.  BEST AMOUNTS WERE FOCUSED ALONG THE
WESTERN SIDE OF THE KEWEENAW PENINSULA WHERE THE LONG FETCH ACROSS
THE WATER IMPACTS ROUGH TERRAIN RIGHT NEAR THE LAKE SHORE.  WE
FOCUSED A MDT RISK OF A FOOT IN THIS AREA WITH RISKS AT THE 4 AND
8 INCH THRESHOLD COVERING MUCH OF THE U.P. AND LOWER MI. 

NEW ENGLAND...

A COMPLICATED MIXTURE OF PTYPES WILL CONTINUE MOVING NORTHWARD
ACROSS NEW ENGLAND AS LOW PRESSURE MOVES FROM SOUTHERN NEW ENGLAND
ACROSS ME AND NEW BRUNSWICK DURING BY FRI EVE.  PCPN HAD BECOME
PREDOMINANTLY LIQUID ACROSS SOUTHERN NEW ENGLAND IN RESPONSE TO A
MODERATELY STRONG LLJ WHICH WAS TRANSPORTING ABUNDANT MOISTURE AND
WARM AIR INTO THE REGION.  SUFFICIENTLY COLD/DRY AIR WILL REMAIN
IN PLACE ACRS INTERIOR NEW ENGLAND FOR MAINLY SNOW...BUT THERE
WILL BE A WARM LAYER AT 85H ASSOC WITH THE LLJ ENERGY WHICH SHOULD
NOSE INTO AT LEAST SOME OF THE INTERIOR SECTIONS OF CNTRL AND NRN
NEW ENGLAND BEFORE THE PCPN ENDS DURING THE DAY.  THIS SHOULD
ALLOW FOR SOME CHANGEOVER TO SLEET AND FREEZING RAIN ALTHOUGH THE
MAIN PCPN TYPE SHOULD BE SNOW. AREAS CLOSE TO THE COAST ARE LIKELY
TO REMAIN RAIN BEFORE THE PCPN ENDS. USING ESSENTIALLY A BLEND OF
THE 00Z GFS AND 21Z SREF...AND THIS CONTINUES TO WARRANT A MDT TO
HIGH RISK OF 4 INCHES ACRS PARTS OF CNTRL AND ESP NRN NEW ENGLAND
WITH A RISK OF 8 INCHES IN ME.
 
THE PROBABILITY OF SIGNIFICANT ICING IS LESS THAN 10 PERCENT.


DAY 2...

GREAT LAKES...

LAKE EFFECT SNOWS WILL CONTINUE...ESPECIALLY IN THE LEE OF LAKES
SUPERIOR AND MICHIGAN..AS ARCTIC AIR PLUNGES INTO THE REGION. 
INSTABILITY WILL BE MAXIMIZED ACRS ESP LAKES SUPERIOR AND MICHIGAN
WITH A POOL OF 85H TEMPS DOWN TO AS LOW AS -25C AND LOCALLY
COLDER. EXPECT BANDS OF VERY HVY LAKE EFFECT SNOW ACROSS FAVORED
PARTS OF THE MI UPPER PENINSULA AND WRN LOWER MI WITHIN THE DEEPER
LYR WNW FLOW.

SRN APPALACHIANS/SRN MID-ATLANTIC...

THE 00Z GUIDANCE DID LITTLE TO HELP PROVIDE CLARITY TO AN
UNCERTAIN FORECAST FOR THE REGION.  THE GFS AND NAM BOTH SHIFTED
THEIR OPINION OF THE STRENGTH AND TRACK OF THE SFC LOW.  IN THE
END...THE NAM WAS AN OUTLIER AND WAS NOT USED IN FAVOR OF THE GFS
SINCE THE 00Z GUIDANCE HAD TENDED TOWARDS A MORE SUPPRESSED
SOLUTION.  CONSEQUENTLY...THE ASSOCIATED PRECIPITATION WAS FURTHER
SOUTH AND WEAKER WHEN COMPARED WITH QPF FROM THE 17/12Z RUN.  WE
OPTED TO INDICATE A RISK OF 4 INCH AMOUNTS ACROSS PARTS OF THE
CAROLINAS IN DEFERENCE TO THE STRONG SHEAR ASSOCIATED WITH THE
ENTRANCE REGION OF A 150 TO 170 KT JET AT H25...BUT DID NOT GO AS
WET AS THE 17/12Z GUIDANCE WOULD HAVE SUGGESTED.  WHILE NOT SHOWN
IN THE PROBABILITY MAPS SINCE AMOUNTS ARE LESS THAN 4
INCHES...THERE IS A RISK FOR MINOR ACCUMULATIONS EXTENDING BACK
INTO PARTS OF GULF COAST REGION AS THE LOW AND THE UPPER JET PULLS
AWAY.  OF SOME CONCERN IS THE FACT THAT TEMPERATURES WHICH FAVOR
DENDRITIC GROWTH ARE MORE OUT OF SYNCH AND THE FACT THAT THE MORE
SUPPRESSED SOLN TENDED TO BE FASTER IN MOVING THE SYSTEM AWAY.
CONSEQUENTLY...WE INDICATED A RISK OF 4 INCH AMOUNTS FROM THE MTNS
OF NC/SC INTO PARTS OF THE PIEDMONT.  

NRN ROCKIES...

DEEP LYR NWLY FLOW WILL ALLOW ADDITIONAL SHRTWV ENERGY AND A
STRONGER CLIPPER SYS TO DROP DOWN FROM WRN CANADA ON SAT. EXPECT
SUFFICIENT MID LVL MOISTURE TO REMAIN IN PLACE FOR ADDITIONAL MDT
TO LOCALLY HVY OROGRAPHICALLY FOCUSED SNOWFALL. THE MAIN THREAT
SHOULD BE FROM THE BITTERROOTS SEWD INTO THE TETONS WHERE A LOW TO
MDT RISK OF 4 INCH AMTS IS INDICATED.

THE PROBABILITY OF SIGNIFICANT ICING IS LESS THAN 10 PERCENT.


DAY 3...

GREAT LAKES...

FRIGID TEMPS ALOFT AND FAVORABLE WINDS FOR LAKE EFFECT SNOW WILL
BE IN PLACE EARLY IN THE PERIOD...THEN START TO MODERATE. 
CONSEQUENTLY...WE HAVE INDICATED A LESSER RISK OF SNOWFALL AT THE
4 AND 8 INCH AMOUNTS AND NOT INCLUDED A RISK AT THE 12 INCH
THRESHOLD. 

NRN ROCKIES/HIGH PLAINS...

THE AFOREMENTIONED SHRTWV DROPPING INTO THE NRN ROCKIES ON DAY 2
WILL DIG MORE TO THE SOUTH TWD THE GREAT BASIN ON SUN. THIS WILL
SUPPORT ADDITIONAL SNOWFALL...ESPECIALLY ACROSS THE MORE FAVORED
OROGRAPHIC LOCATIONS INCLUDING THE SAWTOOTH...TETONS...BIG HORNS
AND SOUTH INTO NRN CO NEAR THE FLAT TOPS. A TIGHT PRES GRADIENT
WITH STRONG LOW LEVEL ELY UPSLOPE FLOW IS FCST TO SET UP BY THE
GFS AND ECMWF THIS PD AS STG ARCTIC HIGH PRESSURE FILTERS SOUTH
FRM WRN CANADA. A LOW TO MDT RISK OF 4 INCHES IS INDICATED ATTM
WITH SOME OF THE SNOWFALL LIKELY TO SPREAD OUT INTO THE IMMEDIATE
HIGH PLAINS TOO.

THE PROBABILITY OF SIGNIFICANT ICING IS LESS THAN 10 PERCENT.

BANN
$$